How To Find A Percentage On A Calculator, Step By Step
By The Calcumatix Team Reviewed by Calcumatix Editorial Review 4 min read
Quick Answer
To find a percent of a number on a calculator, type the number, press multiply, enter the percent, then press the percent button. On a calculator with no such button, divide the percent by one hundred first, then multiply by the number to reach the same result.
Most people grab a calculator to work out a percent, then freeze at the percent button. You only need two methods, and both are quick. This guide shows the button method and the decimal method. It then covers a percent of a number, comparing two values, and adding or taking off a percent. Every example lists the exact keys and the working, so you can copy it on any device.
What Does The Percent Button On A Calculator Do?
The percent button turns your number into a fraction of one hundred, then applies it to the value on screen. On most phones, pressing 80, times, 20, then the percent key returns 16. The button acts differently across calculators, mostly with adding and taking off. The Open University’s OpenLearn maths course says to check how your own device treats the key. If you would rather skip the keys, the percentage calculator does the same maths in one step.
How Do You Find A Percentage Of A Number?
To find a percent of a number, turn the percent into a decimal, then multiply. This decimal method works on every calculator, even one with no percent key. You divide the percent by one hundred. Then you multiply that decimal by your number.
Follow these steps to find any percent of a number:
- Write down the percent and the number you want part of.
- Divide the percent by one hundred to get its decimal.
- Press the multiply key on your calculator.
- Enter the number you want the percent of.
- Press equals and read the result.
Example: Finding 20 percent of 80
Turn the percent into a decimal: 20 / 100 = 0.2. Then multiply: 0.2 × 80 = 16. So 20 percent of 80 is 16. That is a whole number, so no rounding is needed. On a device with a percent key, 80 × 20 % returns the same answer.
How Do You Find What Percent One Number Is Of Another?
To find what percent one number is of another, divide the part by the whole. Then multiply by one hundred. This answers a score out of a total, or a saving against a first price.
Example: What percent is 45 of 180?
Divide the part by the whole: 45 / 180 = 0.25. Then multiply by one hundred: 0.25 × 100 = 25. So 45 is 25 percent of 180. The division is exact to two decimals, so no rounding is needed.
Some tasks come up again and again. The table below lists the keys for each one. Keep it near you until the keystrokes feel easy.
| Task | What to type | Result |
|---|---|---|
| 20% of 80 | 80 × 20 % | 16 |
| 45 as a percent of 180 | 45 ÷ 180 × 100 | 25 |
| Add 15% to 200 | 200 × 1.15 | 230 |
| Take 15% off 200 | 200 × 0.85 | 170 |
How Do You Add Or Subtract A Percentage On A Calculator?
To add or take off a percent, work out the percent amount first. Then add it to, or take it from, the first number. This is how you handle tax, a tip, a discount, or a price rise. A faster route times the first number by one plus or one minus the decimal.
Example: Adding 15 percent to 200
Find the decimal: 15 / 100 = 0.15. Multiply: 200 × 0.15 = 30. Then add it back: 200 + 30 = 230. The shortcut 200 × 1.15 = 230 does both steps at once. To take 15 percent off, use 200 × 0.85 = 170, with no rounding needed.
How Do You Reverse A Percentage On A Calculator?
To reverse a percentage, divide by one plus or one minus the decimal. This finds the first number, before a rise or a cut. It is the move you need when only the final figure is known. A common case is stripping tax back out of a total.
Example: Finding the price before a 15 percent rise
A price is 230 after a 15 percent rise, and you want the original. Divide by one plus the decimal: 230 / 1.15 = 200. So the first price was 200. To undo a 15 percent cut instead, divide by 0.85, so 170 / 0.85 = 200. Both are exact, so no rounding is needed.
Which Method Should You Use On Your Calculator?
Use the decimal method when you want a result you can trust anywhere. Use the percent button when you want speed on a device you know. The decimal method never surprises you, since you control every step. The button is quicker, but it assumes you have tested it first. For money, treat the decimal method as your default, then check it against the Calcumatix maths calculators.
Sources And Notes For The Percentage Calculator Guide
The methods and formulas in this guide come from set maths references:
- The Open University, OpenLearn, Finding Percentages Using A Calculator, on the percent button and the divide-by-one-hundred method.
- Khan Academy, Percent Word Problems, for the standard part-over-whole percentage formula.
For the short site reference version, see the formula reference.
Frequently asked questions
Why does my calculator give a different answer?
Calculators differ in how the percent key treats adding and taking off, so the same keys can return different numbers. Many phone calculators read 200 + 10 % as a ten percent rise and show 220. Test your device with a known sum, or use the decimal method, which acts the same everywhere.
How do you turn a percentage into a decimal?
Divide it by one hundred, which moves the decimal point two places to the left. For example, 20 percent becomes 0.2, and 7.5 percent becomes 0.075. You then multiply by this decimal to find a percent of a number.
Can you find a percentage without a percent button?
Yes. Divide the percent by one hundred, then multiply by your number. For instance, 30 percent of 50 is 0.3 times 50 = 15. This is why the decimal method is the more portable of the two.
How do you find a percentage on a phone calculator?
Type the number, the multiply key, the percent, then the percent symbol. For example, 80 times 20 % shows 16 on most phone calculators. If the app hides the percent key, turn the phone sideways for the wider layout, or fall back on the decimal method.
How do you work out a percentage increase?
Subtract the old value from the new one, divide that gap by the old value, then multiply by one hundred. If a price goes from 50 to 65, that is (65 - 50) / 50 times 100 = 30 percent.
What is the formula for finding a percentage?
The part divided by the whole, times one hundred. So to see what percent 45 is of 180, you work out 45 / 180 times 100 = 25. To reverse it and find a percent of a number, multiply the number by the percent as a decimal.
Does the decimal method work in a spreadsheet too?
Yes. Spreadsheets such as Google Sheets and Excel store a percent as its decimal value internally, then display it with percent formatting. Typing 0.2 into a cell and formatting it as a percent shows 20%, the same decimal the calculator method uses. This is why the decimal method transfers directly from a calculator to a spreadsheet formula.